Gas engines have advantages and disadvantages over glow. The decision to go gas is really not based on size. The large glow engines today have taken that option away. Gas engines actually have less power per displacement than an equivalent glow engine. The advantages are: ease of operation, clean exhaust, hot exhaust (for smoke), reliable idle, virtually no inflight engine failure, low operating costs. Disadvantages: high initial cost, weight,and VIBRATION! Honestly, I prefer gas for ease of operation and cleanliness, but I HATE the vibration.